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Microplastics as carrier for polycyclic aromatic hydrocarbons? A case study investigating the relevance of the carrier effect for human health
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Researchers exposed human intestinal cells in a lab to a harmful chemical (benzo(a)pyrene) alone, mixed with tiny plastic particles, or attached to the particles. Cells showed less response to the chemical when it was carried by plastic, suggesting the plastic did not strongly increase its effects, though some chemical still built up in cells when plastic was present.
Abstract Microplastics (MPs) in the environment can act as carriers for a wide range of pollutants, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and heavy metals, potentially enhancing exposure to these substances. While numerous studies have investigated the ecotoxicological impacts of MP-associated contaminants, their potential impact on human health remains largely unexplored. Testing the so-called carrier hypothesis in human-relevant models is therefore crucial to assess possible implications for human health. In our study, we first conducted a general screening for cytotoxicity and reactivity of a wide range of environmentally relevant MPs (polyamide (PA), polyethylene (PE), polyurethane (PU) and thermoplastic polyurethane (TPU)). Since ingestion represents a major exposure route for humans, the human intestinal Caco-2 cell culture model was chosen. In a second step, we investigate the carrier effect of benzo( a )pyrene (B( a )P), as a representative PAH, for polydisperse PA-6 MPs with a mean diameter (D 50 ) of 7 µm (PA-6 7µm ). For this purpose, cells were exposed for 24 h to the following conditions: (i) untreated cells as control, (ii) PA-6 7µm only, (iii) B( a )P-loaded PA-6 7µm , (iv) B( a )P only and (v) B( a )P + PA-6 7µm in a co-exposure. The concentration of B( a )P adsorbed to PA-6 7µm. was quantified by gas chromatography mass spectrometry (GC-MS) to ensure that the doses administered by treatments (ii)-(iv) were equal. Two complementary approaches were employed to investigate the carrier hypothesis . Firstly, we assessed the cytochrome P450 1A1 (CYP1A1) induction in CaCo-2 cells by quantitative reverse transcription polymerase chain reaction (RT-qPCR). Secondly, we quantified cell-associated B( a )P in CaCo-2 cells as well as B( a )P in cell culture medium using GC-MS. The highest CYP1A1 induction was observed with B( a )P alone, followed by co-exposure and B( a )P-loaded PA-6 7µm . This suggests only a minor relevance of the carrier effect, due to limited bioavailability of B( a )P when adsorbed to PA-6. The quantification of cell-associated B( a )P by GC-MS indicated that co-exposure to B( a )P and PA-6 7µm may enhance cellular B( a )P levels in presence of particles.
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